Burner and method for partly oxidising a gas stream comprising hydrogen sulphide and ammonia

ABSTRACT

The invention concerns a Claus furnace gas burner consisting of at least five concentric tubes (T 1 -T 5 ), forming five concentric gaps for introducing gas, the first tube (T 1 ) being the tube with the smallest diameter and the fifth tube (T 5 ) being the one with the largest diameter, wherein: the ends on the side of the Claus furnace of the third, fourth and fifth tubes are in the same plane, the two central tubes (T 1,  T 2 ) are integral relative to each other and mobile along a central longitudinal axis of the burner relative to the other tubes (T 3 -T 5 ), their ends on the Claus furnace side not exceeding the plane formed by the ends of the three other tubes, the gap formed between the first and second tubes (T 1,  T 2 ) being terminated on the Claus furnace side by an injector oriented towards the periphery of the burner in the injecting direction of the gases into the burner. Depending on the ammonia content of the ammonia-containing gas to be treated in the Claus furnace, the two central tubes (T 1,  T 2 ) are displaced to obtain total elimination of ammonia.

[0001] The invention relates to a gas burner for a Claus furnace,composed of at least five concentric tubes (T1-T5), forming fiveconcentric spaces for the introduction of gas, the first tube (T1) beingthe tube of smallest diameter and the fifth tube (T5) being that of thelargest diameter, in which:

[0002] the ends on the side facing in the Claus furnace of the third,fourth and fifth tubes lie in the same plane;

[0003] the two central tubes (T1, T2) are fastened together and able tomove along the central longitudinal axis of the burner with respect tothe other tubes (T3-T5), their ends on the side facing the Claus furnacenot being able to pass beyond the plane formed by the ends of the threeother tubes; and

[0004] the space formed between the first and second tubes (T1, T2)terminates, on the side facing the Claus furnace, in an injectororiented towards the periphery of the burner in the direction ofinjection of the gases into the burner.

[0005] Depending on the ammonia content of the ammonia-containing gas tobe treated in the Claus furnace, the two central tubes (T1, T2) aremoved so as to obtain complete removal of the ammonia.

[0006] The present invention relates to a burner and to a partialoxidation process, in a Claus furnace, for a stream of gas comprisinghydrogen sulphide and ammonia by reaction with a stream of oxygen-richgas.

[0007] Gas streams rich in hydrogen sulphide are waste gases produced bymany industries, especially the oil refining industry and the productionof natural gas. Especially for environmental reasons, these gases richin hydrogen sulphide cannot be released as such into the atmosphere. Itis therefore necessary to treat them for the purpose of substantiallyreducing their hydrogen sulphide content. A process well known fortreating these gases rich in hydrogen sulphide is the modified Clausprocess, commonly called the Claus process.

[0008] This process comprises a thermal part and a catalytic part. Inthe thermal part, two main reactions are carried out. The first reactionconsists in reacting a portion of the hydrogen sulphide with oxygen inorder to produce water and sulphur dioxide in the following manner:

H₂S+3/2O₂

H₂O+SO₂  (i)

[0009] By this first reaction, approximately ⅓ of the hydrogen sulphideto be treated is oxidized. The remaining ⅔ are reacted with the sulphurdioxide formed during the above first step, according to the followingreaction, called the Claus reaction:

2H₂S+SO₂

3/2S₂+2H₂O  (ii)

[0010] The combustion products are then cooled in a heat recovery boilerand then in a first condenser in which the elemental sulphur isrecovered in liquid form. The gases are then reheated to a temperatureallowing them to be treated on one or more catalytic beds (each of thesebeds being followed by a condenser). The Claus reaction continues on thecatalytic beds until a hydrogen sulphide degree of conversion isobtained which is compatible with the standards governing the dischargeof sulphur dioxide coming from the final step of the process, which isthe incineration of the residual H₂S. In the case in which two or threecatalytic beds do not allow the sulphur dioxide discharge standards tobe reached, a tail gas treatment unit may be added before the wastegases are sent to the final incinerator.

[0011] Refinery-treated gas streams rich in hydrogen sulphide maysometimes contain ammonia in addition to hydrogen sulphide. This is thecase, for example, with the waste gases resulting from acid-waterstrippers in which the condensates of the processes (for example, thehydrocracking or catalytic cracking step in particular in the case ofhigh hydrodesulphurization charges) are steam-stripped so as to recoverthe hydrogen sulphide and the ammonia. Typically, these gases arecomposed of one third hydrogen sulphide, one third ammonia and one thirdwater vapour.

[0012] During the treatment of these gas streams by the Claus process,the destruction of the ammonia therein must be as complete as possiblein order to avoid severe operational problems in the Claus unit. This isbecause, downstream of the heat recovery boiler, deposits of ammoniumsalts in the cold lines or on the output side of the condensers maycause blockages, degradation in the performance of the unit andeventually an increase in sulphur dioxide emissions. When the Clausprocess is being implemented, the ammonia may be destroyed by variouschemical reactions (oxidation, thermal dissociation) which take place atthe same time as the first reaction (i) of the Claus process.

[0013] It is recognized that destruction of the ammonia present in thegases containing hydrogen sulphide is favoured by a high temperature.This destruction may be implemented with Claus oxidation processesinvolving only air or processes involving both air and oxygen.

[0014] In oxidation processes involving only air, the treatment of thegases containing hydrogen sulphide and ammonia may be carried out:

[0015] either by using a two-zone furnace with by-pass of a portion orof all of the gases not containing ammonia. This solution makes itpossible to increase the temperature of the first zone in which all ofthe gas containing ammonia is oxidized. Its drawback is that it cancause poor destruction of the hydrocarbon- or amine-type contaminantspresent in the gas not containing ammonia and create problems other thanthe deposition of ammonium salts (for example, coking of the downstreamcatalysts);

[0016] or by using refinery fuel gas to increase the temperature in thereaction furnace. The major drawback with this operation is the increasein the amount of gas passing through the unit, something which mayresult in a bottleneck. In addition, introducing refinery fuel gas intothe Claus furnace has a tendency to increase the CS₂ and COS contents inthe case in which the fuel gas contains a great deal of CO₂ in the gasescoming from the Claus furnace, and this results in a lowering in theperformance of the catalytic beds downstream of the furnace.

[0017] In oxidation processes involving both air and oxygen, that is tosay in which the combustion air is replaced with an air/oxygen mixture,it is possible to obtain better treatment of the gases containinghydrogen sulphide and ammonia, since the enrichment of the combustionair with oxygen increases the temperature in the reaction furnace andthus improves the destruction of the ammonia. However, in this case, notonly is the temperature of the gases containing ammonia increased, butalso that of the gases not containing ammonia; the amount of oxygen usedis therefore not optimized. Furthermore, the temperature obtained is notalways compatible with the metallurgical characteristics of the burnerused.

[0018] To solve the problem of the use of oxygen specifically toincrease the temperature of the gas containing ammonia, specific burnershave been proposed which allow a separate feed:

[0019] for the air;

[0020] for the pure oxygen or for the oxygen-enriched air;

[0021] for the gases containing ammonia; and

[0022] for the gases not containing ammonia.

[0023] Using these specific Claus burners, allowing separate confinementof the streams of the various gases, it has been possible to obtainhotter or cooler zones inside the flame. This allows localizedtemperature increases dedicated to the destruction of ammonia and makesit possible at the same time to maintain a “cooler” temperature for theoxidation of the other gases and in contact with the refractories of thefurnace. This type of burner is disclosed, for example, in theapplications EP-A1-0 810 974 and EP-A1-0 974 552.

[0024] The dimensioning of these Claus burners is carried out, amongother characteristics, on the basis of a reference ammonia-containinggas having an average ammonia content and an average flow rate. The term“dimensioning” is understood essentially to mean the diameters of thetubes feeding the burner with the various gases. However, depending onthe operating conditions of the refining units located upstream of theClaus unit (for example a severity of the hydrocracker or thehydrodesulphurization unit), the ammonium content of the gas to betreated may vary greatly, temporarily or otherwise, in relation to thecontent of the reference ammonia-containing gas. For example, for arefining site comprising a hydrocracker, depending on whether thishydrocracker is operating or not, the ammonia content of the gas to betreated may vary between 15 and 35%. This variation may also be due topoor operation of the acid-water stripping unit (for example malfunctionof the condenser). The amount of oxygen to be injected in order tocompletely destroy the ammonia is then different and therefore thedimensioning of the Claus burner must be different if it is desired toobtain optimum removal of the ammonia in the Claus unit. However, tochange the dimensions of the burner means changing the burner itself,something which cannot be envisaged for each appreciable change in thegas to be treated.

[0025] The problem of the present invention is therefore to respond tothe variations in the average characteristics of the ammonia-containinggas, especially its NH₃ content, to be treated in a Claus burner withseparate gas feeds.

[0026] One objective of the present invention is to provide an oxidationprocess in a Claus furnace allowing complete destruction of the ammonia.

[0027] Another objective is to provide an oxidation process in a Clausfurnace allowing complete destruction of the ammonia whatever theaverage ammonia content of the gas to be oxidized.

[0028] To meet these objectives, the invention relates firstly to a gasburner for a Claus furnace, composed of at least five concentric tubes(T1-T5), forming five concentric spaces for the introduction of gas, thefirst tube (T1) being the tube of smallest diameter and the fifth tube(T5) being that of largest diameter, in which:

[0029] the ends on the side facing the Claus furnace of the third,fourth and fifth tubes lie in the same plane;

[0030] the two central tubes (T1, T2) are fastened together and able tomove along the central longitudinal axis of the burner with respect tothe other tubes (T3-T5), their ends on the side facing the Claus furnacenot being able to pass beyond the plane formed by the ends of the threeother tubes; and

[0031] the space formed between the first and second tubes (T1, T2)terminates, on the side facing the Claus furnace, in an injectororiented towards the periphery of the burner in the direction ofinjection of the gases into the burner.

[0032] Further features and advantages of the invention will becomeapparent on reading the description that follows. Embodiments andmethods of implementation of the invention are given as non-limitingexamples, illustrated by the appended drawings in which:

[0033]FIG. 1 is a schematic partial section of the end of a burneraccording to the invention;

[0034]FIG. 2 is a schematic front view of a burner according to theinvention; and

[0035]FIG. 3 is a detail of a burner according to the invention.

[0036] The invention therefore relates to a burner for introducing gasesvia five different channels separated from one another by coaxial tubes.On one side, the ends of these tubes run into the Claus furnace wherethe injected gases are burnt. On the other side, each of these tubes isconnected to a gas supply. The three larger-diameter tubes (T3, T4, T5)are stationary. The ends on the side facing the furnace of these threetubes lie in the same plane perpendicular to the central axis of thetubes. The two smaller-diameter tubes (T1, T2) are fixed relative toeach other and their ends on the side facing the furnace lie in the sameplane perpendicular to the central axis of the tubes, but thecombination of these two tubes can move relative to the three othertubes. Thus, this combination of two tubes can slide along the centralaxis of the tubes, which also corresponds to the central longitudinalaxis of the burner, and in both directions of this axis. However, thisforward or rearward movement does not lead on the side facing thefurnace to the ends of the two smaller-diameter tubes passing beyond theends of the three other tubes.

[0037] This movement of the two central tubes (T1, T2) may be obtainedby any means known to those skilled in the art and especially using amechanical bellows which is generally placed at the opposite end ofthese two tubes from the furnace. This bellows may be positioned so thatthe longitudinal axis of the bellows is parallel to the first and secondtubes (T1, T2) and so that the first end of the bellows is stationaryand the second end of the bellows can move and cooperate with the outerwall of the second tube (T2). Thus, by compressing or extending thebellows, the second end of the bellows cooperating with the outer wallof the second tube (T2) will in its movement drive the second tube (T2)and the first tube (T1), since the latter is fastened to the second tube(T2). This mechanical bellows is generally controlled by means of ascrew which, depending on the direction in which it rotates, compressesor extends the bellows and therefore advances or retracts the centraltubes (T1, T2).

[0038] According to the invention, the injector that terminates thespace formed between the first and second tubes (T1, T2) must have ashape such that the gas introduced into it is directed towards theperiphery of the burner in the direction of injection of the gases intothe burner. Such an injector may be obtained by an inflexion of the endson the side facing the furnace of the first and second tubes towards theperiphery of the burner. The injector may also be in the form of a metalring drilled with at least one ring of orifices (C₁₋₂). The expression“ring of orifices” is understood to mean orifices all placed at anequidistance from the central axis of the burner. According to apreferred embodiment, the metal ring is drilled with two concentricrings (C1, C2) of orifices oriented towards the periphery of the burnerin the direction of injection of the gases into the burner. Forpractical reasons, all the orifices of the same ring of orifices aregenerally oriented at the same angle relative to the central axis of theburner. However, the orifices may also be oriented at different angles,this embodiment allowing better mixing of the gases by a turbulenceeffect. If, for each of the two concentric rings of orifices, all theorifices of the same ring of orifices are oriented at the same anglerelative to the central axis of the burner, then the angles of theorifices of the two concentric rings of orifices are preferablydifferent and the difference between these angles of orientation is atleast 5°. Thus, the orifices of the smaller ring of orifices may beoriented towards the periphery of the burner at an angle of between 5and 45° relative to the central axis of the burner. The orifices of thelarger ring may be oriented towards the periphery of the burner at anangle of between 10 and 50° relative to the central axis of the burner.The space formed between the first and second tubes is usually connectedat the opposite end from the furnace to a supply of a gas containinghydrogen sulphide and ammonia, called ammonia-containing gas.

[0039] A pilot burner may be placed in the first tube, the diameter ofthis pilot burner having to be less than that of the first tube so as tobe able to introduce an ignition gas (refinery fuel gas) into theremaining free space of the first tube. In general, when the first tubeT1 is moved, its movement does not cause the pilot burner to move.

[0040] The space formed between the second and third tubes (T2, T3) isusually connected to a supply of an oxygen-containing gas.

[0041] Preferably, the outermost space formed between the fourth andfifth tubes (T4, T5) terminates, on the side facing the Claus furnace,in an injector oriented towards the centre of the burner in thedirection of injection of the gases into the burner. Such an injectormay be obtained by an inflexion of the ends on the side facing thefurnace of the fourth and fifth tubes towards the centre of the burner.The injector may also be in the form of a metal ring closing off thisspace and drilled with at least one ring of orifices for passage of thegas present in this space. These orifices are drilled in the metal ringso that they are oriented towards the centre of the burner in thedirection of injection of the gases into the burner. For practicalreasons, it is preferable for all the holes in the ring of orifices tobe oriented at the same angle relative to the central axis of theburner. However, the orifices may also be oriented at different angles,this embodiment allowing better mixing of the gases by a turbulenceeffect. Before the orifices of the same ring of orifices are oriented atthe same angle relative to the central axis of the burner, then theseorifices of the ring are preferably oriented towards the centre of theburner at an angle of between 5 and 45°, even more preferably between 10and 20°, relative to the central axis of the burner. The cross sectionof these orifices may be of any shape. The space formed between thefourth and fifth tubes is usually connected to a supply of a gascontaining hydrogen sulphide but not ammonia, called acid gas.

[0042] According to an alternative embodiment of the invention, theburner includes an intermediate tube (T3′) placed between the third tube(T3) and the fourth tube (T4). This intermediate tube (T3′) isstationary like the third, fourth and fifth tubes (T3, T4 and T5) andits end on the side facing the furnace lies in the same planeperpendicular to the central axis of the third, fourth and fifth tubes(T3, T4 and T5). According to this alternative embodiment, the spaceformed between the third tube (T3) and the intermediate tube (T3′)preferably terminates on the side facing the Claus furnace in aninjector oriented towards the centre of the burner in the direction ofinjection of the gases into the burner. Such an injector may be obtainedby an inflexion of the ends on the side facing the furnace of the thirdtube (T3) and of the intermediate tube (T3′) towards the centre of theburner. On the side facing the furnace, the injector may also be in theform of a metal ring (C_(3-3′)) closing off the end of this space anddrilled with at least one ring of orifices for passage of the gaspresent in this space. These orifices are drilled in the metal ring sothat they are oriented towards the centre of the burner in the directionof injection of the gases into the burner. For practical reasons, it ispreferable for all the orifices in a ring of orifices to be oriented atthe same angle relative to the central axis of the burner. However, theorifices may also be oriented at different angles, this embodimentallowing better mixing of the gases by a turbulence effect. If all theorifices of the same ring of orifices are oriented at the same anglerelative to the central axis of the burner, then these orifices arepreferably oriented towards the centre of the burner at an angle ofbetween 5 and 45° relative to the central axis of the burner. Theseorifices may have any shape.

[0043] According to the latter alternative embodiment, the space formedbetween the third tube (T3) and the intermediate tube (T3′) and thespace formed between the third and fourth tubes (T3, T4) may beconnected to the same supply of an oxygen-containing gas. In general, avalve is placed between the supply of the oxygen-containing gas and thespace formed between the third tube (T3) and the intermediate tube(T3′).

[0044] The diameters of the five tubes and the diameters of the orificesin the rings (injectors) are defined according to the velocities in thetubes and to the ratios of the velocities at the nose of the burner thatit is desired to give each of these gases injected into the burner. Thevelocities in the tubes depend on the average flow rates of the streamsentering the burner. The flow rates of the oxygen-rich gases dependdirectly on their oxygen concentration, on the flow rates of the streamsof acid gases and on the average NH₃ content of the ammonia-containinggas. The average flow rates of the streams are set by the refinery inwhich the process of the invention is carried out, which is itselflimited by the treatment possibilities of the Claus unit (dimensions ofthe Claus furnace and characteristics of the heat exchanger placed atthe outlet of the said Claus furnace). Depending on these parameters, aperson skilled in the art is perfectly capable of determining thediameters of the tubes and the diameters of the orifices so that thedesired velocities and velocity ratios are obtained.

[0045] In general, the diameters of the orifices of the rings must besuch that:

[0046] the ratio of the velocity of the ammonia-containing gas to thevelocity of the oxygen-rich gas is between 0.1 and 0.8 or between 1.2and 5, the velocities being taken at the end of the burner on the sidefacing the furnace; and

[0047] the ratio of the velocity of the acid gas to the velocity of thegas less rich in oxygen is between 0.1 and 0.8 or between 1.2 and 5, thevelocities being taken at the end of the burner on the side facing thefurnace.

[0048] The burner according to the invention is preferably made of anaustenitic alloy containing chromium and a high nickel content.

[0049] The invention also relates to a first partial oxidation processin a Claus furnace for a stream of gas containing hydrogen sulphide andammonia, referred to as ammonia-containing gas, and for a stream of gascontaining hydrogen sulphide and no ammonia, referred to as acid gas,using a stream of oxygen-containing gas, in which process:

[0050] the burner defined above is used;

[0051] if the NH₃ content of the ammonia-containing gas to be treated isgreater than the average NH₃ content of the ammonia-containing gas forwhich the burner is designed, the central tubes (T1, T2) are positionedso that their ends on the side facing the furnace lie in a planedifferent from that of the ends of the other tubes (T3-T5);

[0052] if the NH₃ content of the ammonia-containing gas to be treated isless than or equal to the average NH₃ content of the ammonia-containinggas for which the burner is designed, the central tubes (T1, T2) arepositioned so that their ends on the side facing the furnace lie in thesame plane as that of the ends of the other tubes (T3-T5);

[0053] the ammonia-containing gas is injected into the space formed bythe first and second tubes (T1, T2);

[0054] the acid gas is injected into the space formed by the fourth andfifth tubes (T4, T5);

[0055] an oxygen-rich gas is injected into the space formed by thesecond and third tubes (T2, T3); and

[0056] a gas less rich in oxygen is injected into the space formed bythe third and fourth tubes (T3, T4).

[0057] The burner used in this first process has the features of theburner defined above. Furthermore, this burner is designed for completeelimination of the ammonia contained in the ammonia-containing gas whichis introduced into it and is so for an average value of the NH₃concentration in the ammonia-containing gas, the ammonia beingcompletely removed for this average value when the central tubes (T1,T2) are pushed completely towards the end of the burner on the sidefacing the furnace, referred to as the forward position.

[0058] According to this first process of the invention, when anappreciable change in the operating conditions of the Claus unit, owingto the presence of ammonia, or of the refinery units producing theammonia-containing gases is observed, the average NH₃ content in theammonia-containing gas to be treated is measured. Depending on thedifference between the measured value of the NH₃ concentration of theammonia-containing gas to be treated and the average NH₃ concentrationvalue of the ammonia-containing gas for which the burner is designed,the ends of the central tubes (T1, T2) are positioned relative to theends of the other tubes (T3-T5) corresponding to the end of the burneron the side facing the furnace. Thus, the ends on the side facing thefurnace of the central tubes (T1, T2) are moved further away from theends on the side facing the furnace of the other tubes (T3-T5) if themeasurement of the NH₃ content in the ammonia-containing gas to betreated is greater than the average NH₃ concentration value of theammonia-containing gas for which the burner is designed. The centraltubes of the furnace are therefore moved back. This operation has theeffect of allowing, at the ends of the two central tubes (T1, T2) on theside facing the furnace, the ammonia-containing gas to be treated to bemixed with a gas richer in oxygen, and therefore of increasing thetemperature of the flame at this point and of consequently increasingthe ammonia conversion yield. It is therefore possible to respond to theincrease in ammonia concentration in the ammonia-containing gas to betreated and to obtain effective destruction of this species withoutchanging burner. On the other hand, if the measurement of the NH₃content in the ammonia-containing gas to be treated is less than orequal to the average NH₃ concentration value of the ammonia-containinggas for which the burner is designed, the central tubes are pushedtowards the end of the burner on the side facing the furnace, so as toplace the ends on the side facing the furnace of all the tubes (T1-T5)in the same plane and thus allow mixing of the ammonia-containing gas tobe treated with a gas less rich in oxygen.

[0059] This first process according to the invention is generallyimplemented in a conventional Claus furnace.

[0060] According to this first process, a burner that includes anintermediate tube (T3′) may be used, for which a valve is placed betweenthe supply of gas less rich in oxygen and the space formed between thethird tube (T3) and the intermediate tube (T3′), as described above.When such a burner is used, the opening of the valve placed between thespace formed between the third tube (T3) and the intermediate tube (T3′)and the supply of gas less rich in oxygen may be controlled according tothe flow rate of the acid gas, especially during the start-up phase ofthe unit or during the phase of stopping the oxygen feed.

[0061] This first process according to the invention applies to any typeof ammonia-containing gas. In general, the hydrogen sulphideconcentration in the stream of ammonia-containing gas is generallybetween 10 and 90 mol %; the ammonia concentration in this stream of gasis generally greater than or equal to 5 mol % and preferably between 10and 60 mol %. This gas may also contain 10 to 60 mol % of water vapour.

[0062] In the first process according to the invention, theoxygen-containing gases may be air or oxygen-enriched air, the latterbeing preferably enriched with a content of greater than 25 mol %, evenmore preferably a content of between 40 and 100 mol %, the gas enrichedto 100% oxygen corresponding to pure oxygen. The oxygen content to whichthe said gas is enriched with oxygen corresponds to the molar fractionof oxygen of the said enriched gas. To take an example, air enriched to50% oxygen consists of a gas mixture comprising 50 mol % oxygen.According to a preferred embodiment, the oxygen-rich gas isoxygen-enriched air, or pure oxygen, and the gas less rich in oxygen isair. When the burner used includes an intermediate tube (T3′) betweenthe third and fourth tubes, the gas less rich in oxygen may beintroduced simultaneously into the space formed by the third tube andthe intermediate tube and into the space formed by the intermediate tubeand the fourth tube. These two spaces are connected to the same supplyof gas less rich in oxygen.

[0063] According to the first process of the invention, the ammoniacontent of the gas containing hydrogen sulphide and not ammonia,referred to as acid gas, is less than 5 mol % (<5%). The hydrogensulphide concentration in this gas stream may itself be at least 10 mol%, and more generally between 60 and 95 mol %. The stream of acid gasessentially consists of hydrogen sulphide and at least one of thefollowing compounds: water vapour, carbon dioxide, hydrocarbons andother sulphur compounds.

[0064] The invention also relates to a second partial oxidation processin a Claus furnace for a stream of gas containing hydrogen sulphide andnot ammonia, referred to as acid gas, using at least one stream ofoxygen-containing gas, in which:

[0065] the burner defined above is used;

[0066] the acid gas is injected into the space formed by the first andsecond tubes (T1, T2) and into the space formed by the fourth and fifthtubes (T4, T5); and

[0067] at least one oxygen-containing gas is injected into the spaceformed by the second and third tubes (T2, T3) and into the space formedby the third and fourth tubes (T3, T4).

[0068] This second process is generally implemented as an alternative tothe first process described above when the ammonia-containing gas is notavailable, for example during the shut-down of the refining unitsproducing ammonia-containing gas. In this case, the acid gas isintroduced instead of the ammonia-containing gas into the space formedby the first and second tubes (T1, T2) in addition to its usualintroduction into the space formed by the fourth and fifth tubes (T4,T5).

[0069] Simultaneously with the introduction of the acid gas, at leastone oxygen-containing gas is injected into the spaces formed by thesecond and third tubes (T2, T3) and by the third and fourth tubes (T3,T4). It is possible either to introduce the same oxygen-containing gas(generally air) into these two spaces or to introduce gases havingdifferent oxygen concentrations, as was described in the operation ofthe first process according to the invention.

[0070]FIGS. 1, 2 and 3 illustrate the burner and the first processaccording to the invention. The burner consists of six concentric tubes(T1, T2, T3, T3′, T4, T5) forming six concentric spaces. At the end onthe side facing the furnace:

[0071] the space formed by the first and second tubes (T1, T2) runs intotwo rings of orifices (C1, C2), the said orifices having a circularcross section;

[0072] the space formed by the third tube (T3) and the intermediate tube(T3′) runs into a ring of orifices (C_(3-3′)), the said orifices havinga circular cross section; and

[0073] the space formed by the fourth and fifth tubes (T4, T5) runs intoa ring of orifices (C₄₋₅), the said orifices having an oval crosssection.

[0074] At the end of the space formed by the first and second tubes (T1,T2), all the orifices of the ring of smaller diameter (C1) are orientedtowards the periphery of the burner at the same angle relative to thecentral axis of the burner and all the orifices of the larger-diameterring (C2) are oriented towards the periphery of the burner at the sameangle relative to the central axis of the burner. At the end of thespace formed by the third tube and the intermediate tube (T3, T3′), allthe orifices of the ring (C_(3-3′)) are oriented towards the centre ofthe burner at the same angle relative to the central axis of the burner.At the end of the space formed by the fourth and fifth tubes (T4, T5),all the orifices of the ring (C₄₋₅) are oriented towards the centre ofthe burner at the same angle relative to the central axis of the burner.

[0075] A pilot burner (5) is placed in the first tube (T1) in order toignite the flame. A refinery fuel gas (7) is also introduced into thisspace in order to ignite the flame and to maintain it.

[0076] A bellows (6) is fixed at its end (61) to the tube (T2) and atits other end (62) to the stationary tube (T3). A screw (63) allows thebellows to be compressed or extended.

[0077] The following are introduced into the burner:

[0078] the gas containing hydrogen sulphide and ammonia (1) in the spaceformed by the first and second tubes (T1, T2);

[0079] the oxygen-rich gas (2) in the space formed by the second andthird tubes (T2, T3);

[0080] the gas less rich in oxygen (3) in the space formed by the thirdtube (T3) and the intermediate tube (T3′) and in the space formed by theintermediate tube (T3′) and the fourth tube (T4); and

[0081] the acid gas (4) in the space formed by the fourth and fifthtubes (T4, T5).

[0082] If the value of the ammonia content of the ammonia-containing gasis greater than the average ammonia content of this gas set for thedesign of the burner, then the central tubes (T1, T2) are pushed backtowards the rear position by operating the screw controlling thedisplacement of the bellows. If thereafter the value of the ammoniacontent of the ammonia-containing gas becomes close to or less than theaverage ammonia content of this gas set for the design of the burner,then the central tubes (T1, T2) are pushed into the forward position byoperating this same screw.

1. Gas burner for a Claus furnace, composed of at least five concentrictubes (T1-T5), forming five concentric spaces for the introduction ofgas, the first tube (T1) being the tube of smallest diameter and thefifth tube (T5) being that of largest diameter, in which: the ends onthe side facing the Claus furnace of the third, fourth and fifth tubeslie in the same plane; the two central tubes (T1, T2) are fastenedtogether and able to move along the central longitudinal axis of theburner with respect to the other tubes (T3-T5), their ends on the sidefacing the Claus furnace not being able to pass beyond the plane formedby the ends of the three other tubes; and the space formed between thefirst and second tubes (T1, T2) terminates, on the side facing the Clausfurnace, in an injector oriented towards the periphery of the burner inthe direction of injection of the gases into the burner.
 2. Burneraccording to claim 1, characterized in that the central tubes (T1, T2)are moved by means of a mechanical bellows.
 3. Burner according to claim1 or 2, characterized in that the injector terminating the space formedbetween the first and second tubes (T1, T2) is in the form of a metalring drilled with at least one ring of orifices (C1, C2).
 4. Burneraccording to claim 3, characterized in that the injector terminating thespace formed between the first and second tubes (T1, T2) is in the formof a metal ring drilled with two concentric rings (C1, C2) of orificesoriented towards the periphery of the burner in the direction ofinjection gases into the burner.
 5. Burner according to claim 4,characterized in that, for each of the two concentric rings (C1, C2) oforifices terminating the space formed between the first and second tubes(T1, T2), all the orifices of the same ring are oriented at the sameangle relative to the central axis of the burner.
 6. Burner according toclaim 5, characterized in that the angles of the orifices of the twoconcentric rings (C1, C2) of orifices terminating the space formedbetween the first and second tubes (T1, T2) are different and thedifference between these angles of orientation is at least 5°.
 7. Burneraccording to one of claims 4 to 6, characterized in that the orifices ofthe smaller ring (C1) terminating the space formed between the first andsecond tubes (T1, T2) are oriented towards the periphery of the burnerat an angle of between 5 and 45° relative to the central axis of theburner.
 8. Burner according to one of claims 4 to 7, characterized inthat the orifices of the larger ring (C2) terminating the space formedbetween the first and second tubes (T1, T2) are oriented towards theperiphery of the burner at an angle of between 10 and 50° relative tothe central axis of the burner.
 9. Burner according to one of thepreceding claims, characterized in that a pilot burner (5) is placed inthe first tube (T1).
 10. Burner according to one of the precedingclaims, characterized in that the outermost space formed between thefourth and fifth tubes (T4, T5) terminates, on the side facing the Clausfurnace, in an injector oriented towards the centre of the burner in thedirection of injection of the gases into the burner.
 11. Burneraccording to the preceding claim, characterized in that the injectorterminating the space formed between the fourth and fifth tubes (T4, T5)is in the form of at least one metal ring drilled with at least one ringof orifices (C₄₋₅).
 12. Burner according to the preceding claim,characterized in that the orifices of the ring of orifices (C₄₋₅)terminating the outermost space formed between the fourth and fifthtubes (T4, T5) are oriented towards the centre of the burner at an angleof between 5 and 45° relative to the central axis of the burner. 13.Burner according to one of the preceding claims, characterized in thatit includes an intermediate tube (T3′) placed between the third tube(T3) and the fourth tube (T4).
 14. Burner according to the precedingclaim, characterized in that the space formed between the third tube(T3) and the intermediate tube (T3′) terminates, on the side facing theClaus furnace, in an injector oriented towards the centre of the burnerin the direction of injection of the gases into the burner.
 15. Burneraccording to the preceding claim, characterized in that the injectorterminating the space formed between the third tube (T3) and theintermediate tube (T3′) is in the form of a metal ring drilled with atleast one ring of orifices (C_(3-3′)).
 16. Burner according to thepreceding claim, characterized in that the orifices of the ring(C_(3-3′)) terminating the space formed between the third and fourthtubes (T3, T4) are oriented towards the centre of the burner at an angleof between 5 and 45° relative to the central axis of the burner. 17.Burner according to one of claims 13 to 16, characterized in that thespace formed between the third tube (T3) and the intermediate tube (T3′)and the space formed between the third and fourth tubes (T3, T4) areconnected to the same supply of oxygen-containing gas.
 18. Burneraccording to the preceding claim, characterized in that a valve isplaced between the supply of oxygen-containing gas and the space formedbetween the third tube (T3) and the intermediate tube (T3′).
 19. Partialoxidation process in a Claus furnace for a stream of gas containinghydrogen sulphide and ammonia, referred to as ammonia-containing gas(1), and for a stream of gas containing hydrogen sulphide and no ammonia(4), referred to as acid gas, using at least one stream ofoxygen-containing gas (2, 3), in which process: the burner according toone of claims 1 to 18 is used; if the NH₃ content of theammonia-containing gas to be treated is greater than the average NH₃content of the ammonia-containing gas for which the burner is designed,the central tubes (T1, T2) are positioned so that their ends on the sidefacing the furnace lie in a plane different from that of the ends of theother tubes (T3-T5); if the NH₃ content of the ammonia-containing gas tobe treated is less than or equal to the average NH₃ content of theammonia-containing gas for which the burner is designed, the centraltubes (T1, T2) are positioned so that their ends on the side facing thefurnace lie in the same plane as that of the ends of the other tubes(T3-T5); the ammonia-containing gas (1) is injected into the spaceformed by the first and second tubes (T1, T2); the acid gas (4) isinjected into the space formed by the fourth and fifth tubes (T4, T5);an oxygen-rich gas (2) is injected into the space formed by the secondand third tubes (T2, T3); and a gas less rich in oxygen (3) is injectedinto the space formed by the third and fourth tubes (T3, T4). 20.Process according to claim 19, characterized in that the burneraccording to claim 18 is used and in that the opening of the valveplaced between the space formed between the third tube (T3) and theintermediate tube (T3′) and the supply of gas less rich in oxygen (3) iscontrolled according to the flow rate of the acid gas (4).
 21. Processaccording to either of claims 19 and 20, characterized in that theoxygen-containing gases (2, 3) are oxygen-enriched air with a content ofgreater than 25 mol %, preferably a content of between 40 and 100 mol %.22. Process according to one of claims 19 to 21, characterized in thatthe oxygen-rich gas (2) is pure oxygen.
 23. Partial oxidation process ina Claus furnace for a stream of gas containing hydrogen sulphide and noammonia (4), referred to as acid gas, using at least one stream ofoxygen-containing gas (2, 3), in which process: the burner according toone of claims 1 to 18 is used; the acid gas (4) is injected into thespace formed by the first and second tubes (T1, T2) and into the spaceformed by the fourth and fifth tubes (T4, T5); and at least oneoxygen-containing gas (2, 3) is injected into the space formed by thesecond and third tubes (T2, T3) and into the space formed by the thirdand fourth tubes (T3, T4).